Behaviors of bearing capacity of ultra-long bored piles

Based on the comparison and analysis of the static load tests on the experimental ultra-long bored piles of CCTV Tower and World Trade Center Tower (third stage) in Beijing, the behaviors of the pile tip resistance and the shaft resistance are studied. The results show that the deformation of pile top is mainly from its compression under loads. The tip resistance makes minor contribution to the bearing capacity relative to the shaft resistance. The pile shaft resistance exhibits a softening phenomenon in clay layer and a hardening phenomenon in sandy soil layer, and its play exhibits depth effect. The bearing capacity distribution of piles estimated according to the specifications is greatly different from the test results. Both the effective cleaning residue process and the post grouting means are proposed to be necessary measures for the ultra-long bored piles.